Generally, an electrophotographic printing machine includes a photoconductive member which is charged to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to an optical light pattern representing the document being produced. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the document. After the electrostatic latent image is formed on the photoconductive member, the image is developed by bringing a developer material into proximal contact therewith. Typically, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted to the latent image from the carrier granules and form a powder image on the photoconductive member which is subsequently transferred to a copy sheet. Finally, the copy sheet is heated or otherwise processed to permanently affix the powder image thereto in the desired image-wise configuration.
In the prior art, both interactive and non-interactive development has been accomplished with magnetic brushes. In typical interactive embodiments, the magnetic brush is in the form of a rigid cylindrical sleeve which rotates around a fixed assembly of permanent magnets. In this type of development system, the cylindrical sleeve is usually made of an electrically conductive, non-ferrous material such as aluminum or stainless steel, with its outer surface textured to improve developer adhesion. The rotation of the sleeve transports magnetically adhered developer through the development zone where there is direct contact between the developer brush and the imaged surface, and toner is stripped from the passing magnetic brush filaments by the electrostatic fields of the image.
In the prior art, for two component magnetic brush development systems, the trim blade typically comprises an angled, straight edge blade spaced from the surface of the developer roll along the length thereof. The trim blade consists of a metal substrate. The trim blade is oriented so that the edge portion of the blade contacts developer particles on the surface of the development roll in order to smooth the layer of developer particles and control the mass of developer on the roll.
A significant disadvantage to conventional trim blades is that they deteriorate rather quickly. Particularly, the surface of the blade that contacts the developer particles tends to wear down over time. As the trim blade member is responsible for creating a uniform layer of developer across the developer roll, a deteriorated or worn trim blade compromises print quality. A constant gap between trim blade and developer roll must be maintained. When a trim blade wears indicated by degradation in the quality of the final image, it is necessary for a customer to replace it with a new trim blade or adjust the spacing between the developer roll and the trim blade to achieve the correct developer mass on the sleeve of the development roller. Often, this involves replacing a number of system elements that are collectively provided in a Customer Replaceable Unit (CRU). When a trim blade wears out, the entire CRU must be replaced, which is an expensive and time-consuming process.
The above problem is more acute in semiconducting magnetic brush systems (SCMB) that consist of thin brushes (low mass on sleeve, MOS) close spacing to the latent image and conductivity of the carrier midway between conductive and insulative. These systems are able to operate at very high speeds using low voltages. In these systems the MOS is controlled by a trim blade comprised of two parts, a non-magnetic structural part and a soft magnetic part which couples to the magnetic field of the developer roll. This magnetic part of the trim blade is spaced from the developer roll along its length and leads to a very uniform thin layer of developer on the development roll surface. The MOS is a critical parameter which controls solid area, background and line quality. This CP is factory adjusted and the process is designed to be fairly insensitive to variation in MOS. However, failure modes exist in which material and/or roll surface and/or metering blade age leads to variation in MOS which in turn leads to degraded image quality making it difficult to maintain color quality consistently over time and between marking engines. A current solution to this problem is to replace the worn development system components. Another problem comes in trying to clear developer from SCMB magnetic rolls in multipass systems; currently one needs to cam the development system away from the photoreceptor which adds expensive components.